Module validity 

Which values in a vector are not null.

spec/07-execution.md section 7.1: validity has three representations and the distinction is load-bearing. All valid is the absence of a mask and gets the fastest kernels. All invalid is a flag and short circuits entirely. Anything else is a bitmap.

Photon’s published result is that separate no-null kernels are worth a measurable amount on real data, because real data is mostly not null. The cost of knowing which case you are in is one branch per vector rather than one per value, which is why the three cases are an enum here rather than a bitmap that happens to be all ones.

Structs

Bitmap

One bit per value, set meaning valid.

Enums

Validity

Which values in a vector are valid.